1. Field of the Invention
The present invention relates to electrophotographic copying machines of the transfer type, and more particularly to such a copying machine wherein a reciprocating member, such as a reciprocating optical system or reciprocating original carriage, is used for exposing a photoconductive member to the image of an original.
2. Description of the Prior Art
The reciprocating member of electrophotographic copying machines generally perform a scan movement for the exposure of an original and a return movement to the start of the scan position or stationary position. The distance of the reciprocation is conventionally controlled by systems which can be divided generally into two types: one wherein the distance of movement of the reciprocating member is controlled according to the size of paper used for copying, and the other wherein the distance is controlled according to the size of the original or to the size specified by the user for the original.
However, these systems have been found to involve various drawbacks for use in copying machines of improved performance which are adapted for copying, for example, at an increased speed or at a variable magnification.
The control system according to the paper size has the drawback that when paper of large size is used for copying a small original, the reciprocating member uselessly moves also over an area beyond the original, i.e., an area which need not be scanned. The idle movement increases the distance of return movement for the next copying cycle to result in a reduced copying speed. The reduction of the copying speed becomes pronounced in a multi-copying operation.
On the other hand, when the control system according to the size of original is used for multi-copying a small original on paper of large size, the reciprocating member scans a distance corresponding to the size of the original and thereafter returns, but if the copy sheet has not been completely transported before the start of the subsequent scan movement, the reciprocating member must be stopped temporarily until the completion of the transport. Otherwise, another sheet will be fed to overlap the preceding sheet. However, if the reciprocating member is stopped temporarily, the problem of vibration arises when the member is initiated into the subsequent scan movement. Such vibration is avoidable by increasing the pre-scanning distance from the start of scan position to the start of exposure position, but a reduced copying speed will then result. The vibration further adversely affects the drive system and other neighboring devices to shorten their life.
Generally the vibration produced is greater when the reciprocating member is initiated into the scan movement from a stopped position then when it is brought into the scan movement continuously from the return movement. Accordingly the vibration can be reduced if the reciprocating member is not stopped at the start of a scan position. U.S. Pat. No. 3,554,640 discloses a reciprocating original carriage which is adapted to stop at the end of a scan movement, then is started from this position toward the start of a scan position and continuously brought into a scan movement from the return travel. The present applicant proposes in U.S. patent application Ser. No. 177,636 filed on Aug. 8, 1980 a reciprocating member which is brought into preliminary reciprocation at the start of a scan position without any exposure and thereafter is caused to perform a scan movement continuously with the return travel for reciprocation movement during exposure. The reciprocating member can be initiated into the scan movement very smoothly by being biased toward the scan direction with the force accumulated by the return travel and also by being given a drive force for scanning with appropriate timing. With the proposed system, unlike the system of U.S. Pat. No. 3,554,640, the reciprocating member is started at the start of a scan position because a signal emitted during the scan movement of the member is utilized for starting a feeding of a sheet so that the leading end of the sheet can be accurately registered with the image on the photoconductive member. Although the proposed system has the advantage that the scan movement can be initiated very smoothly, the exposure making reciprocation requires the preceding preliminary reciprocation, with the result that if the system is used in combination with the foregoing system wherein the reciprocating member is controlled to move a distance in accordance with the size of original and is adapted to stop temporarily at the start of a scan position to avoid the overlap of sheets, each copying cycle requires two strokes of reciprocation which reduce the speed of the copying operation. Incidentally, the embodiment of the U.S. patent application includes a reciprocating member which moves a distance according to the paper size and continuously travels in reciprocation for multi-copying. The member therefore performs only one stroke of preliminary reciprocation without any exposure.